1. Field of the Invention
The present invention relates to a two-layer structure composite material, comprising a piezoelectric material and a structural material, for detecting cracks in a structural material with the purpose of predicting destruction.
2. Description of Prior Art
Structural ceramic materials are fragile, and some treatment is needed when high reliability is required. In this respect, there are strong demands on a new type of ceramics, in which functional ceramics is combined with structural ceramics which generates a signal when cracks occur and contributes to the prediction of the possible destruction of the material before it actually occurs. Such the prediction of destruction is needed not only for structural ceramics but also for general structural materials, in which cracks may occur.
To detect cracks in structural materials, an acoustic emission method is normally used. In this case, it is necessary to set a large sensor on a structural material. However, in case sufficient space is not available to set the sensor, or in case a structural material is rotating at high speed, it is not possible to identify the occurrence of cracks and hense it is necessary for the prediction of possible destruction to disassemble and inspect a material at regular interval.